Postscript...

I went out after dinner to take a photo of a card, and C was inside doing the dishes. So when I heard the cheeping robin, I called to him to come and pick up the camera. I'd better make sure the settings are more suitable next time, or else let him feed the bird and take photos myself, but he did a pretty good job.
This one cheeps more and more - it's only a guess, but my theory is that it's the female, and she is making verbal contact with the chicks in the nest, because I don't think it's far off, just in the hedgerow beyond the end of the wall. Certainly when they were feeding each other, I am sure it was the female who did the cheeping back then. But it's a safe bet that the cheeping one will come to our hands straight away, while the other is more hesitant and may not come at all, but make a foray into the porch instead.

The European robin is much smaller than the North American robin, only about 5" long, and weighing about half to three-quarters of an ounce, and both sexes are the same. The American robin is part of the thrush family. I can see why Colin Tudge, in his Secret Life of Birds says that there is a lot of confusion in the current taxonomy of birds.